1. Field of the Invention
The present invention relates to a cordless telephone system in which a battery of a mobile unit is chargeable from a cordless charger.
2. Description of the Prior Art
There has been so far known a cordless telephone system of multi-channel type which comprises a base unit connected to a wired line (public line) and a mobile unit coupled with the base unit through a spatial communication circuit and which controls call transmission and reception between the base and mobile units on a control channel and then detects idle one of a plurality of speech channels to realize a speech.
In such a cordless telephone system, in order that the mobile unit can talk with the party at an arbitrary position away from the base unit, the mobile unit incorporates a chargeable battery therein as its operational power source and the battery is designed to be charged through a charging mechanism of the base unit when the mobile unit itself is mounted on the base unit.
Referring to FIG. 9, there is schematically shown an arrangement of such a prior art cordless telephone system as stated above, which comprises a base unit 1 connected to wired lines (public line) 2 and a mobile unit 3 coupled with the base unit 1 through a spatial communication circuit 4. Connected to the base unit 1 is a power source adapter 6 which converts an AC voltage of a commercial AC power source 5 into a DC voltage. When the mobile unit 3 is mounted on the base unit 1, the base unit 1 supplies an output voltage from the power source adapter 6 to the mobile unit 3 to charge a battery housed within the mobile unit 3.
The aforementioned arrangement, however, imposes such a use restriction that the base unit 1 must be connected with the wired lines 2 and also be installed at such a specific location that can be connected with the commercial AC power source 5. For this reason, such an arrangement that the battery of the mobile unit 3 must be charged from the power source adapter 6 of the base unit 1, is inconvenient in handling.
To overcome such an inconvenience, there has been suggested a charge-only charger which is provided as a device separated from the base unit and which uses a commercial AC power source to charge the battery of the mobile unit 3.
However, the aforementioned charge-only charger, though it can be charged at a location different from the installation location of the base unit 1, must be positioned at a place close to a commercial AC power source, which results in that, in an outdoor field or such a place where it is difficult to have access to the commercial AC power source it becomes impossible to charge the charger. Thus, in the case where the battery of the mobile unit 3 is decreased down to its to-be-charged level beyond its normal charge level, it is disadvantageously required to carry the mobile unit 3 to a place where the charger is disposed close to the commercial AC power source.